No, it's not necessary but you can choose cut the shroud and make a hack job of it, or just remove it. Removing it, won't affect the cooling performance of the VN.
Update of the VN VT Snorkel You Tube Video;
B S1 day ago
Are your putting the Upper panel back on because you're actually having a problems with cooling or is it because, you're being influenced by comments to do so? Have you checked underhood temps and IAT's? Are you getting higher temp gauge readings?
I have to say, I'm going to look at this logically and much closer.
First off: we don't really know why the Youtuber Synergy Media is; reinstalling the Upper Cowling other than he says it's, "Crucial for cooling." I'm curious as to why he determined it was crucial to cooling the VN; without specifying actual temperature readings, under the hood before and after & actual engine temperature readings before and after. It's easy enough to do and explain.
Second: In the article, the cardboard top panel or cowling was placed over the radiator and condenser. This is nearly exactly to the top cover which is placed over the radiator and condenser on the VN, attached to the bumper. It's never removed. So the VN is still identically compliant to the article posted. So are the other two top and bottom panels, consistent with the article which are installed the VN.
The VN radiator shroud is never removed and is still in place. The top panel on the bumper, which reattaches to the chassis, will disallow and air taking the path of least resistance, over the radiator. Thus channeling it thru the radiator and condenser as before.
In essence, the bumper cover is the acting the same as the cardboard panel displayed in the article. Unless there is an air gap between the top cover and the radiator. I'll have to look closely..................
Ok, after looking at the rear of the radiator shroud, the top of the engine, and the sides of the upper panel, there is no appreciable air gaps for air to pass around or over the top of the condenser and radiator. Condenser being at the forefront and radiator behind. @8:17 on the video, you can see the full frontal portion of the condenser, lower panel and intercooler.
With the radiator shroud intact, and the upper panel removed; the radiator is still completely inclosed. I verified this on my own VN. There are only two small gaps on either side where the upper panel is removed and the condenser line pass thru on the right.
I'd be surprised to see these small gaps causing and appreciable differences with cooling, taking in consideration the radiator, is still fully enclosed in the shroud. Also keeping in mind air cannot pass over the radiator with the chassis member and bumper top cover in place. Pretty interesting considering, if these two small air gaps might actually cause an issue.
The only way to accurately determine if there is an issue, is to install without and with. I'll check both and take temp measurements. Now, is it necessary to reinstall the radiator top cowling, or just to block the small air gaps with the appropriate panels.
If required, creating sheet metal panels are a simple task, even easier custom cutting the upper panel. No great chore either way.